Experimental warming affects soil carbon dynamics in boreal and temperate forests: a meta-analysis

Boreal and temperate forests, spanning cold mid- to high-latitude environments and encompassing about 43% of the global forest area, are highly vulnerable to warming. Understanding the response of soil carbon (C) dynamics in these forests to warming is of paramount importance, yet significant uncertainty remains. In this meta-analysis, data from 97 studies across 65 sites were synthesized to investigate the effects of warming on soil C inputs, pools, and outputs in boreal and temperate forests. Our results reveal that warming increased aboveground biomass (by 33%) and litterfall (by 15%), while decreasing litter mass remaining (by 7%), with no significant change observed in fine root biomass. Furthermore, warming led to a 9% increase in soil total respiration and a 15% increase in autotrophic respiration, yet had no discernible impact on soil organic carbon (SOC) content. The methods, magnitude, and duration of warming were found to regulate the responses of soil C dynamics. Buried heater warming elicited the most pronounced effects among warming methods. Additionally, soil total respiration exhibited an acclimation response to warming magnitude and duration, while litter decomposition rates increased and SOC content and microbial biomass C decreased with escalating warming magnitude. Moreover, greater soil respiration response occurred in temperate forests than in boreal forests. These findings underscore the nuanced and context-dependent nature of soil C dynamics in response to experimental warming, providing critical insights for understanding the role of boreal and temperate forests in future climate change mitigation strategies.